Multilayer photographic elements



y 1947- o. 'WEMURRAY 2,423,465

MULTILAYER PHOTOGRAPHIC ELEMENTS Filed Dec. 15, 1944 LUE-SENSITIVE EMULSION ELATIN-SILVER FERROCYANIDE ORTHO CHROMATIC EMULSION ELAI'IN-SILVER DICHROMATE PANCHROMATIC EMULSION GELAI'INI-PHENOL CELLULOSE ACETATE BLUE SENSITIVE EMULSION GELATIN-SILVER PHOSPHATE (YELLOW) PANCHROMATIC EMULSION CELLULOSE NITRATE BLUE SENSITIVE EMULSION ELATIN YELLOW DYE 1 j REEN SENSITIVE EMULSION 1 jj GELATIN-PHENOL CELLULOSE ACETATE GELATIN-PHENOL ELATIN-SILVER SULFATE 5 GREEN-BLINDRED SENSITIVE EMULSION ,O l is Ell lard INVENTOR.

' ZTIJRNLY Patented July 8, 1947 d UNITED STATES PATENT OFFICE MULTELAYER LPHOTOGRAPHIC ELEMENTS Application December 15, 1944, Serial No. 568,234

7 Claims.

This invention relates to color photography and, more particularly, to novel elements and processes for producing multicolor pictures. Still more particularly, it relates to multilayer elements for recording color images which contain novel light-barrier layers.

An object of this invention is to provide an improvement in the art of color photography. A more specific object is to provide new multilayer elements for the recording of color images. A further object is to provide new photographic elements for reversal processes of color photography. A further object is to provide multilayer photographic elements with light-barrier-forming layers. A related object is to provide such layers which are substantially free from light absorbing properties prior to development. Another object is to provide such layers from economical and available materials. A still further object is to provide such layers which form a uniform, dense black stratum upon development, which is substantially opaque to the printing light used during the second exposure of a reversal process. Still other objects will be apparent from the following description of the invention and the attached drawing.

Multilayer film elements which contain prefogged silver salt layers between difierentially sensitive silver salt layers are known. Their preparation and use in reversal processes of photographic development are described in U. S. Patents 2,191,502; 2,262,055 and 2,319,369. These elements, when exposed to a colored object and developed, have two or more color separation silver image layers containing both silver and unexposed, undeveloped silver salts and an intervening layer of metallic silver. The layers containing the color separation images can then be selectively re-exposed and redeveloped (in the presence of a color-former) to form dye images in such layers. Upon removal of the silver and silver salts, a color picture is obtained. When two barrier layers are present, the central lightsensitive layer can be re-exposed by the methods described in the above patents prior to color development.

The novel elements of the present invention contain, in place of the pre-fogged salt layers of the prior art, reducible silver salts which do not evidence any differences in developed silver density between exposed and unexposed areas after a coated layer of such salts has been exposed in a type IIB sensitometer and developed. The salts used are those which do not form developable latent images upon exposure in a ca era or printing device under ordinary latent image-forming exposure conditions. The silver The type IIB sensitometer is described in Journal of the Society of Motion Picture Engineers, vol. 15, 1931, pp. 536-559.

salts comprehended in general are water-insoluble and when incorporated in a layer of a hydrophilic colloid such as gelatin, in contrast to silver halides, do not require exposure to light to make them capable of rapid reduction to metallic silver by ordinary photographic developers, e. ,g., having reduction potentials between 0.3 and 40.0.

The novel elements and layers can be made by incorporating the desired silver salt in a solution of the hydrophilic colloid and subsequently coating it onto the support or a layer or membrane of a photographic element. This may advantageously be accomplished by preparing an aqueous solution or suspension of a water-soluble salt, where the anion is that of the anion of the desired silver salt, and admixing a water-soluble silver salt. After formation, the water-soluble salts can be removed and the resulting solution or dispersion is made available for coating.

In general, the novel elements consist of a transparent support having at least two differentially sensitive photographic layers, one of the layers preferably being imposed directly on the support and being further characterized in that a layer of the reducible silver salts is interposed between the emulsion layers. Of course an adhesive or subbing stratum can be used to anchor the said photographic layer to the support. Various constructions of elements can be made and representative types will be described below and illustrated in the accompanying drawing.

Elements for three-color photography may have three difierentially sensitive silver halide layers, which are so disposed and sensitized that they are adapted to record the red, green, and blue regions of the spectrum, on one side of a transparent base with a light-barrier-forming layer of the above described reducible silver salts between each emulsion layer, or may have two of the sensitive layers on one side of the base and one on the other. In the latter type, only one lightbarrier-forming silver salt layer need be used and this may be placed between the two sensitive layers. However, an additional light-barrier-forming layer can be imposed directly on the base, if desired.

The silver salts used in the light-barrier-iorming layers are preferably colorless. However, they need not be completely colorless. In fact, in some instances they may be colored and used as filter layers as well as light-barrier-forming layers. A light yellow colored salt, for instance, can be used as a light-barrier-iorming layer between a bluesensitive silver halide emulsion layer and a, greensensitive silver halide emulsion layer. Similarly, a light orange or red colored salt can be used as a filter layer between a green sensitive silver halide layer and a red sensitive silver halide emulsion layer. Filter dyes can be added to such light-barrier-formin layers to increase their screening effect, if desired.

The invention will be further illustrated, but is not intended to be limited by the following examples:

Example I Approximately 1000 grams of a suspension of silver ferrocyanide in gelatin are prepared by dissolving 50 grams of silver nitrate in 660 ml. of water and mixing the resulting solution brought to a temperature of about 85 F. with a solution prepared by dissolving 34 grams of potassium ferrocyanide and 15 grains of photographic gelatin in 300 milliliters of water at 115 F. To the mixture is then added an additional 90 grams of gelatin and the resulting suspension is chilled, Washed and otherwise processed according to the usual procedure employed in the manufacture of an ordinary gelatino-silver halide emulsion. When the final product is coated on a suitable support a yellowish, hazy layer is obtained. When said layer is treated with a developing solution containing approximately 3 grams of parahydroxy-methylaniline sulfate, 4 grams of hydroquinone, 30 grams of sodium carbonate and 50 grams of sodium sulfite per liter, the silver Potassium sulfate Potassium thiocyanate Sodium tungstate Sodium arsenate Trisodiurn phosphate Sodium tetraborate Methyl-p-arninophenol sulfate grarns Sodium sulfite (desiccated) do Hydroquinone do Borax dc Water to make ccsn The silver densities resulting in each case were determined on the same instrument. The following readings were obtained:

Type of Gelatin Suspension Density Read Against White Light Density Read Against Blue-Green Light Density upon Development for Five Minutes Density Read Against Red Light Density Read Against Green Light Silver sulfate (clear, colorless) Silver thiocyanate (white) Silver tungstate (yellow) Silver arsenate (orange red) Silver phosphate (yellow). Silver borate (yellow) Ill! ferrocyanide is rapidly reduced to metallic silver producing a practically opaque neutral density Example IV A gelatino-silver halide emulsion was prepared 'u i fi entne layer Whnout prevlous exposure containing approximately 40 grams of mixed sill r i tl ie following exam les silver salt suspen- Yer.ha1ides (95% Silver bromide 5% silver ions are prepared acco ding to the directions loam-e and 9 grams of gelgitm per tar) pensions of silver errocyanide and silver sulfate g1ven in Example I by adding solution A to soluin gelatin were also prepared as described in tion B at the temperatures indicated and then 0 EX m 1 IT (1 II? All 1m 1 8 adding C and processing the mixture in the mani mine-s1 ner known to the art for the preparation of an silver salt emulsions were then coated on cellulose ordinary photographic gelatmmsflver halide nitrate film ease in the manner {HO-1W1). to the art, 1810!? the layer of gelat ne-silver sulfate suspension emu Example H being made approximately three times as thick as the other layers. The gelatino-silver halide Solution A--Temperature 90 F.: emulsion was given a pre-fogging exposure as Silver nitrate grams 50 described in 'Sease et al, U. S. P. 2,191,502. ter Ammonia milliliters 50 the coatings were properly dried density readings Water do 500 v were taken on samples of the undeveloped stoens Solution .BTemperature 120 F.: with white, red, green and blue lights as described Potassium ferrocyanide grarns 34 in the preceding examples, following which sam- Gelatin do 15 pics of the film were developed for two, four and six Water milliliters 230 minute periods in a highly concentrated develop- Substance C: ing bath such as is commonly used in the process- Gelatin "grams" 90 ing of X-ray film. The results were as follows:

. Densityalter Densityafter Densltyafter Type of Emulsion gfg i ngt li g i n st r k g i n s t f iug gi fig %X$ L 1 r Dexitglloglgent White Light Red Light Green Llght Blue Light Minutes Minutes I MinuteS Galatino-silverhalide r. 21 21 2l 24 l. 20 l. 26 l. 30 Silver sulfate .07 .08 .10 l8 2. 6 2. 89 3. 0+ Silverfenocyanide 22 22 .24 36 2. 05 2.19 2. 23+

Example III Example V A variety of gelatin silver salt suspensions were prepared exactly as described in Example II by replacing the potassium ferrocyanide with the following compounds:

The multi-layer film of the type shown in Figure 1 of the drawing was prepared as follows: A cellulose acetate film base l was coated with an aqueous solution of gelatin containing a phenol to form a thin sub-layer 5 On this sub-layer was deposited a gelatino silver bromideiodide panchromatic emulsion containing alpha naphthoseleno carbocyanine ethbromide to form layer 2. An aqueous suspension of gelatin containing silver dichromate was prepared by the method described in Example II by substituting for the potassium-ferro-cyanide thereof 46 grams of potassium dichromate. The resulting gelatin silver dic-hromate layer 3 was deep red in color, thus making the function as a filter layer to protect the red sensitive emulsion layer 2 from the green light transmitted through the upper layers. On layer 3 was then coated a gelatino silver bromide-iodide ortho-chromatic emulsion containing erythrosine or thiopseudocyanine to form a green sensitive emulsion layer i. On the latter layer was deposited a gelatin silver ferro-cyanide suspension substantially identical with that described in Example II save for the addition of Yellow T. Color Index No. 148 to form layer An unsensitized silver bromide-iodide emulsion was then coated to form a blue sensitive emulsion layer 6.

The film just described was placed in a camera and exposed to a color scene with the light havig passed the optical aperture, being first incident on the blue sensitive emulsion layer. The film was then developed in an energetic developer of the following composition:

ZA-diaminophenol hydrochloride grams 7.5 Sodium sulfite do 30.0 Potassium bromide do 1.0 Potassium carbonate do 5.0 Water to make ccs 1000 After development and washing, the film consisted of 3 color separation negative image layers bearing both silver and unexposed silver halide which were respectively separated by two lightbarrier layers containing substantial opaque deposits of metallic silver.

The red-sensitive emulsion layer was then reexposed through the base using a white printing light. The printing light did not effect the other two layers because it wa blocked by the dense silver deposit formed in layer 8 interposed between them and the red-sensitive emulsion layer. The latent reversed image formed in the redsensitive layer 2 was then developed in a bluegreen color forming developer of the following composition:

Z/l-dichloro-alpha naphthol grams 2.5 Diethylparaphenylenediamine hydrochloride do '3 Potassium carbonate do 40 Sodium sulfite do 5 Ethanol milliliters 25 Water to make liters 1 This treatment produced both a silver and a minus-red image in the red-sensitive layer only.

The blue sensitive layer is then exposed to a printing light and developed in a yellow colorforming developer containing 3 grams of acetyl acetone dissolved in 25 milliliters of ethanol, 3 gram of diethylparaphenylenediamine hydrochloride, 3 grams of sodium hydroxide, grams of sodium sulfite and sufiicient water to make one liter of solution. Upon completion of the development a metallic silver image and a yellow dye image was formed in layer 5.

The central ortho chromatic emulsion layer l was then exposed to X-ray radiations for 60 seconds to render the layer developable after which it was developed in a magenta color former developer solution containing 2 grams of lphenyl-3-methyl pyrazolone dissolved in cos. of alcohol, 3 grams of diethyleneparaphenylenediamine hydrochloride, grams of sodium carbonate, 5 grams of sodium sulfite and sufiicient water to make one liter of solution. Upon completion of development a metallic silver image and a magenta dye image were formed in layer l.

The resulting film element was first treated for 10 minutes in an aqueous solution containing 5% of sodium ferricyanide and then treated in an aqueous solution of sodium thiosulfate (30% concentration) after which it was thoroughly washed in water and dried. A 3-color picture in the form of positive dye images was obtained by the above procedure.

Example VI A two-color print film having the structure shown in Figure 2 was prepared a follows: a cellulose nitrate film base 7 was coated with a gelatino silver bromide iodide emulsion containing as a panchromatic sensitizing dye, alpha naphthoseleno carbocyanine ethbromide and diacetoacetamino-l2,4,5-benzo-bis-thiazole to form layer 8. On the latter layer was coated an aqueous suspension of silver phosphate in gelatin prepared in accordance with the procedure given in Example III to produce barrier-forming layer 0. On the latter layer was then deposited a gelatino silver bromide gelatin emulsion to form blue sensitive layer 50. The resulting film was then processed by exposing to blue light the blue sensitive emulsion layer behind a separation positive obtained from the blue-green separation negative of a bipack film.

The silver phosphate layer 9 is yellow in color and acts as a yellow filter layer during the exposure and then prevents the blue light from reaching layer 5.

The panchromatic emulsion layer 8 is then exposed through the base behind the orangered separation positive of the bipack film by means of red light. The exposed film is then I developed in a non color-forming developer of the following composition:

Methyl-p-aminophenol sulfate grams 4.0 Hydroquinone do 7.0 Sodium sulfite (desiccated) do 60.0 Sodium carbonate do 70.0 Potassium bromide do 5.0 Water to make ccs 1000 for 10 minutes which develops the silver phosphate layer to an opaque metallic silver layer and at the same time produces negative silver images in the two silver halide layers corresponding to the positives behind which each was exposed. After washing the blue sensitive emulsion layer alone is exposed to white light (the light being prevented from reaching the other emulsion layer by the opaque metallic silver layer formed on development) and then developed in a blue-green color former of the type described in Example V. After washing the film is then taken into white light and layer 8 is exposed and then developed in a solution of the following composition:

The metallic silver deposits are then removed after the manner described in Example V and the film is washed and dried leaving a twocolor positive print consisting of blue-green and orange-red dye images.

Example VII A multilaye-r color film having the structure illustrated in Figure 3 was prepared as follows: A cellulose-acetate film base ii which was coated on both sides with an aqueou solution of gelatin containing acetic acid and a phenol to form thin sub-layers i2 and 92. On the sub-layer i2 is coated an aqueous gelatin dispersion of silver sulfate prepared as described in Example III. On the latter layer was coated a gelatino silver bromide-iodide emulsion sensitized with pinacyanol or one of the dyes described in United States Patents Nos. 2,148,979, 2,149,890, and 2,- 071,898, to form a green-blind red sensitive emulsion layer it. 011 sub-layer i2 is coated a gelatino silver bromidedodide emulsion containing erythrosine or thiepseudocyanine to form green sensitive emulsion layer 55. On the latter layer was coated a gelatin solution containing a yellow filtering material such as yellow colloidal metallic silver, Tartrazine Color Index No. 640 or one of the dyes described in United States Patent No. 2,255,077 to form yellow filter layer 50. On this layer was deposited a gelatino silver bromide emulsion to form blue sensitive layer 1?.

The resulting film element may be processed in the following manner:

1. Expose the film in a camera to a color scene with the layer ll nearest the light.

2. Develop in a non color-forming developer of the following composition:

2.4 diaminophenol hydrochloridegrams 8.5 Sodium sulfite do 50.0 Potassium bromide do 2.0 Potassium carbonate anhydrous do 8.0 Water to make ccs 1000 3. Expose layer I l to white light and develop in a blue-green color-forming developer of the type described in Example V.

i. Expose layer ii to blue light and develop in a yellow color-forming developer solution of the following composition:

Acetoacetanilide grams 1.0 Diethyl paraphenylenediamine.HCL do 2.0 Sodium carbonate do 200 Potassium bromide do 1.0 Water to make ccs 1000 5. Expose layer in by flashing with white light and develop in a magenta color-forming developer of the following composition:

Meta amino phenylmethylpyrazalone grams 1.0 Diethyl paraphenylenediamine.HCl do 2.5 Potassium carbonate do 15.0 Potassium bromide do 2.0 Water to make ccs 1000 6. Bleach all silver and remove silver salts from the layers by treatment first with an aqueous solution of sodium ferricyanide of 5% concentration and then in an aqueous solution of sodium thiosulfate of 30% concentration.

7. Wash and dry.

The resulting film element contains a multicolor picture corresponding to the original color scene.

Although the silver barrier layers of the present fit invention have been illustrated in the specific examples as having particular applicability to reversal types of multi-layer color films, it is not to be supposed that the invention is restricted thereto. On the contrary, various other types of color films using silver barrier layers fall within the contemplated scope of the invention. For example, the silver salt barrier layers disclosed herein should be of particular value in color processes where differential treatment of various emulsion layers is controlled by inter posing between two layers a layer of hardened gelatin obtained from a silver salt layer which is developed during the first development and then bleached by a. tanning bleach bath to set up a diihcultly permeable layer as known to the art. Such multi layer films may be of the type used in color development or in color bleach-out processes.

In addition to the silver salts which have already been described as developable without prefogging or exposur to light there are a number of others which may be employed in the invention such as silver chro-mate, silver ferricyanide, silver arsenite, silver tartrate, silver citrate, and silver oxalate.

The silver salts useful in this invention do not form developable latent images when given a normal exposure in a camera, etc. They are rapidly reduced to silver salts by using a photographic developing agent having a reduction potential of at least 0.3. This reduction should take place in a period of about 10 minutes. The useful developing agents having a reduction potential of this degree are set forth on page 338 of the Handbook of Photography, by Henney 8t Dudley published by Whittlesey, New York (1939).

The silver salts may be used in the waterpermeable colloid layers over a wid range of proportions. The amount added should be suincient to form a dense metallic silver deposit upon development which prevents normal printing lights from passing therethrough. In general from .1 to 1.5 parts of the salt per part of colloid binding agent is satisfactory.

In the multilayer color films which constitute an important aspect of the invention ther is possibility of wide variation in the arrangement and composition or the various layers and the manner in which they are processed. It is possible for example to employ light-sensitive silver halide layers which are processed to form dye images in a second development of a. reversal process by means of a color developer containing both a color-forming compound and a developing agent or a color former which is resistant to diffusion may be placed in the emulsion layer originally and the dye formed by processing with a colorcoupling developer.

Any color-forming compound known to theart may be used. Suitabl blue-green color formers include ortho-hydroxy di phenyl, chlorophenyl phenol, orthoand metachlorophenol, ortho iodo and orthobromophenol, 2,SA-trichloronaphthol, 2,6-dibromo-1,5-dihydroxy naphthalene, 4,4-di- (1-hydroXy-2naphthoylamino) diphenyl, 1 hydroxy-Z-carboxy 5 dodecylaminonaphthalene, N-stearoyl-N-(1-hydroxy-2 naphthoyl) P phenylenediamine sodium sulfonate, resorcinol mono-n-dodecyl ether (described in United States Patent No. 2,166,181), the product of phydroxybenzoic acid and formaldehyde (described in United States Patent No. 2,323,481) and the product of polyvinyl alcohol and salicylaldehyde (described in United States Patent No.

2,310,943); magneta color formers such as pnitro-benzyl cyanide, o-nitrobenzyl cyanide, ptoluyl-acetonitrile, omega-*cyano-acetyl-dibenzfuran, omega-cyanoacetyl, acenaphthene, 1- omega-cyano-acety1-coumarone, 1 :3-di- (omegacyanoacetyl) benzene, cyanacetophenone, methoxy-alpha-naphthoyl acetonitrile, l-cyanacetamino benzt'hiazole, l naph'thyl-3-methyl-4- pyrazolone, the sodium salt of 1-(3'-sulfo phenyl) S (4"stearoy1 amino phenyl-) 5- pyrazolone, 1- (4'-hydroxy-3'-carboxy-phenyl) B-pyrazolone, 4,4-di(carboyl-l-p-amino-phenyl- 3-methyl-5 pyrazolone) 4,4 bis(3" methylpyrazolonyl-l)-diphenyl (described in United States Patent No. 2,200,924), 4,4-methylene-bis- (m stearoylaminophenyl) methyl pyrazolone, and 4,4-o-sulfo-benzylidenebis(phenyl methyl pyrazolone) (both of which are described in United States Patent No. 2,294,909).

Suitable yellow or orange color formers include the diacylacetamino-aryl-bis-thiozoles of United States Patent No. 2,140,540 particularly difuroyl-aoetamino 1,2,4,5 benzo-bis thiazole, the acylacetarylides of United States Patent No. 2,108,602, B-nap-hthoyl ace-tone, aceto-acetic esters, ethyl-gamma-chloroacetoacetate, ethylalpha chloro-acetoacetate, ethyl malonate, ethyl-p-nitrophenyl acetate, ethyl acetopropionate, ethyl acetone dicarboxylate, furoyl acetic ester, the arylacetamino phenyl morpholines of United States Patent No. 2,133,937, 2-hydroxy-3- naphthoyl amino benzoyl acetanilide, sodium stearolylamino-benzoylacetanilide-p carboxylate, p caproylamino benzoylamino salicycli-c acid, furoylacet-p-amino phenyl amyl ether (United States Patent No. 2,184,303) and dipicolinoylacet-benzidine.

As developing agents for the second, colorforming development the preferred agents are pphenylenediamine derivatives of p-phenylenediamine, e. g., p-aminodimethylaniline, p-aminodiethylaniline, p-aminodibutyl aniline, p-N-meth'yl aminoaniline, p-N-ethyl aminoaniline, p-aminophenol, N :N-diethyl-o-phenylenediamine, chloro-p-phenylenediamin 1,2,5 to-luylenediamine, 2- amino-5-(N-beta hydroxyethyl-N-butyl) aminotoluene and the salts of such compounds particularly the hydrochlorides.

It is not essential that the binding material for the silver salt layers of the invention be gelatin but instead, many other binding materials may be employed. For example, the silver salts developable without prefogging can be dispersed in any convenient hydrophilic layer-forming substance which is water-permeable but substantially Water-insoluble. Such materials include natural and synthetic substances such as gums, resins, cellulose derivatives, carbohydrate derivatives, etc. Specifically there may be mentioned polyvinyl alcohols and esters including polyvinyl acetate and mixtures of such ester with polyvinyl acetals derived from acetaldehyde, isobutyraldehyde, benzaldehyde, etc., various alkyd resins derived from glycerol, ethylene glycol and higher polyhydric alcohols and polybasic acids such as phthalic, maleic, adipic, succinic, etc., and including those alkyd resins described in United States Patent No. 2,290,289. Also there may be used condensation products of phenols, naphthols, or hydroxy aromatic carboxylic or sulfonic acids with bifunctional compounds such as aldehydes, ketones, and dialkylol derivatives, phenols, amides, and amines. In the preparation of the layers the usual photographic coating ingredients 10 such as spreading agents, 1. e., glycerine, saponine, long chain alkyl sulfates, etc., may be used.

The silver-salt barrier layers of the invention may contain a wide variety of modifying ingredients, e. g., filter dyes such as Naphthol Yellow Color Index No. 10, Auramine Color Index No. 655, Eosine Color Index No. 768, Unanine Color Index No. 766, Xylene Red B Color Index No, 748, Rose Bengale Color Index No. 779, Congo Red Color Index No. 370, Carmoisine A Color Index No. 179; filter materials of a colloidal nature such as yellow colloidal silver sulfide and materials to produce a solubilizing efiect on the barrier layers to make them stripping layers. Among the latter materials may be mentioned water soluble or alkali soluble cellulose derivatives, e. g., methyl cellulose, ethyl cellulose, cellulose acetic acid or cellulose glycollic acid and its water soluble salts; water or alkali soluble resins, e. g., polyvinyl alcohol, polyvinyl esters (e. g., formates); alkyd resins, polyamides and water-sensitive polymeric amino-nitrogen containing bodies in- SOlUdblG in water and 5% ammonium hydroxide, but soluble in aqueous acetic acid in the range of about 2 to 5% describe in United States Patent No. 2,182,814.

In the processing of the type of film exemplified by Example V the exposure of the central layer (4) to X-rays in order to make it developable in the color-reversal developer is not the only means that can be used to achieve this end. The purpose can be accomplished chemically by bathing the film in a 5% aqueous solution of sodium arsenite or an organic sulfur bearing compound such as allyl thiourea or hydrogen peroxide. In addition the film can be exposed to mechanical vibrations, e. g., ultrasonics or to the action of heat rays preferably after hardening the emulsion layers in 5% aqueous formaldehyde.

The final bleaching bath employed in the processing of the film to remove all the metallic silver may, as has been mentioned, consist of a two bath solution of Farmers reducer. Other bleach baths however may produce equally satisfactory results, e. g., potassium bromide-ferricyanide bleaches, acid mixtures of potassium "permanganate and potassium dichromate and the sulfamic acidpotassium clichromate bath described in United States Patent No. 2,195,419.

The products of this invention are particularly useful in various methods of color photography. They may be used in two and three color processes and are adaptable to use in the preparation of stripping films for color print processes. Certain of the products lend themselves in admirable fashion to the manufacture of light-barrier layers in which the undeveloped silver salts of the layer erform the additional function of a chromatic filter by virtue of their clear strong colors. The silver-salt suspensions are also useful in the preparation of wide variety of filter layers and antihalation screens or backings, because by varying their preparation and processing metallic silver deposits can be formed by development in different colloidal binding agents of every conceivable color and density. In addition the filter and screening properties of the products may be employed in the manufacture of black and white films with integral filters to eliminate certain bands of the spectrum, e. g., for press, commercial, portrait and scientific photography.

One of the most important advantages of the invention resides in the fact that it permits the preparation of new and useful barrier layers for color photography which are more highly transparent and develop to higher densities than the silver halide emulsion layers known to the art. A related advantage of the invention is derived from the pure strong colors exhibited by some of the undeveloped silver salts used in the preparation of barrier layers. These colors permit the use of silver salt suspensions as chromatic filter layers before development as well as barrier layers after development. A still further advantage of the invention is the elimination of prefogging exposures before development as the compounds of the invention are developable without exposure to light.

What is claimed is:

l. A photographic element comprising a transparent base bearing at least two differentially sensitized silver halide emulsion layers which have disposed therebetween a Water-permeable colloid layer containing unfogged silver salts which transmit light to which one of the said emulsion layers is sensitive and do not form developable images on exposure to light but are rapidly and completely reducible in their unfogged state to metallic silver with a developing agent having a reduction potential of 0.3 to 40.

2. An element as described in claim 1 wherein the silver salts are colorless.

3. An element as set forth in claim 1 wherein at least one emulsion layer contains an immobile color former.

4. A photographic element comprising a transparent base bearing three differentially sensitized silver halide emulsion layers and two water-permeable colloid layers containing unfogged silver salts which transmit light to which one of the said emulsion layers is sensitive and do not form developable latent images on exposure to light but are rapidly and completely reducible in their unfogged state to metallic silver with a devel- 12 oping agent havin a reduction potential of 0.3 to 40, said latter layers being disposed between each of said emulsion layers.

5. An element as described in claim 4 wherein at least one of the silver salts is colored.

6. A photographic element comprising a transparent base bearing three silver halide emulsion layers sensitized to the red, green and blue regions of the spectrum respectively and tWo Water-permeable colloid layers containing unfogged silver salts which transmit light to which one of the said emulsion layers is sensitive and do not form developable latent images on exposure to light but are rapidly reducible in the unfcgged state to metallic silver with a developing agent having a reduction potential of 0.3 to if), said latter layers being disposed between each of said emulsion layers.

'7. A photographic element as set forth in claim 6 wherein the layers are in the order of red, green and blue respectively and the silver salt layer between the blue and green layers is a yellow colored salt.

OTIS WILLARD MURRAY.

CETED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,516,82 i Mannes et a1 Nov. 25, 1924 2,163,325 Sanders-Dolgoruki June 20, 1939 2,191,592 Sease et a l Feb. 27, 1940 2,319,369 Sease et a1 May 18, 1943 FOREIGN PATENTS Number Country Date 505,0Q9 Great Britain May 4, 1939 

